Selective laser melting (also referred to as SLM) is an additive manufacturing process in which a (metal) powder material is melted at defined positions by means of a laser. Selective laser melting enables components to be produced with almost any designable three-dimensional component geometry. In order to produce three-dimensional components, selective laser melting is usually carried out in layers, i.e. form-welding is carried out layer by layer. In this case, the material powder is initially distributed in a thin layer over a base plate. Once the material powder in this first layer of the powder bed has been remelted by the laser at the necessary positions, following the desired contour of the component being produced, and solidified to form a first solid material layer, the base plate is lowered or moved by the amount of the first layer and a new (second) layer is applied. Laser melting is repeated accordingly on this layer, wherein remelted material in what is currently the uppermost layer is connected to solid material disposed directly thereunder. The process described above is repeated until the component to be generated has been completely produced.
So that the completed component can be removed more easily, a comparatively filigree support structure can be built on the base plate or the substrate which supports the actual component. This structure may be manually removed, for example, following removal of the component. Depending on the geometry of the component being generated (in the case of overhangs, for example) further supports or supporting structures may also be generated, where necessary, and may be removed before the component is used.
In this case, laser melting takes place in a processing chamber which is typically hermetically sealed and in which the atmosphere is made as homogeneous as possible, wherein the laser required to melt the powder material enters the processing chamber through a processing chamber window. So that the laser beam is able to act on the powder material at the positions required for the desired component geometry, the laser beam is typically deflected by means of a scanner device.
Due to the continuous laser irradiation, selective heat conduction is required where appropriate, in order to avoid geometric deviations from the desired geometry and, in particular, to avoid solidification cracks caused by thermally induced internal stresses and to eliminate unwanted material structures, in particular, such as coarse grain, for example.
In order to manage or control these detrimental consequences, it is known in the art for the component to be heat-treated once it has been completed by laser melting. According to the disclosure in WO2012/055398 A1, for example, this heat treatment may take place in an external heating appliance (a furnace), into which the component is moved upon completion, or optionally in the processing chamber itself, once the residual, unmelted material powder has been removed.
EP 2 415 552 A1 also discloses the heating of the completed component to optimize the material properties thereof following the selective laser melting process. In this example, heating takes place by means of a heating coil which is produced using the component to be generated in the same selective laser melting process and which is therefore located together with the created component in the material powder. Once the material powder has been removed, the heating coil is connected to an electrical energy source in order to inject the heating power.
The heat management of the resulting component may also be indirectly affected, even during selective laser melting, by heating the base plate for example or introducing heat exchangers for cooling purposes in holding devices. A procedure of this kind is also disclosed in EP 2 415 552 A1, in which the component is supported or held by a holder which cools the workpiece at the point of contact, so that sensitive areas of the component are not exposed to excessively high temperatures.
With an additive manufacturing process in the form of selective electron beam melting (SEBM), in which the material powder is melted instead of a laser beam with the help of an electron beam, the heat conduction may be influenced by deflecting the electron beam in advance of and/or following the actual manufacturing process.
WO2012/055398 A1 further teaches a selective change in the composition of the material of the component produced by selective laser melting through the use of reactive gases in the processing chamber, wherein the change in composition is intended to bring about an increase in the thermal resistance of the component.
In the case of selective laser melting, however, the accessibility of the process zone during generation of the component and therefore the possibility of actively influencing the process locally, i.e. on site, is reduced as a matter of principle.